The present invention relates to the electronic drawing and display arts. It finds particular application in conjunction with tablet computers and will be described with particular reference thereto. However, it is to be appreciated that the present invention will also find application in other high latency drawing systems.
Heretofore, tablet computer systems have commonly included a drawing and display pad, such as a 640.times.480 grid of display cells. A memory array, for example 640.times.480.times.2, stored an indication whether each cell of the memory should be displayed as black or white.
The tablet computer systems further included an electronic writing pen and a pen sensitive surface overlying the display. The writing pen and sensitive surface, along with conventional resolver circuitry provided the x,y-coordinates of the writing pen relative to the coordinate system of the display grid. The x,y-coordinates of the pen were clocked out at regular, short intervals such that the output was a series of x,y-coordinates indicating the trajectory (or stationary position) of the pen.
The trajectory information was transferred by radio, cable,or other data link central computer. The central computer included the processing and drawing software for performing a number of drawing, recognition, or other operations based on the pen input. Typically, a relatively large number of tablet computers were networked with the central computer. After the central computer processed the trajectory information, it calculated appropriate displays to be displayed on the tablet computer screen. Often, but not always, the display included the immediate preceding trajectory of the electronic pen.
One of the drawbacks of the system resided in the latency or time lag between when the pen was moved and when time the central computer caused the local tablet computer to display the trajectory which the electronic pen had followed. Depending on system load, a lag or delay of 1-2 seconds was not uncommon. In 1-2 seconds, a user could write several words or even a complete communication either graphically or textually. Most users found it disconcerting to have no visual feedback as the pen moved. The trajectory was displayed a short time later, often in a sudden burst, i.e., the whole display or recent writings appeared at once.
The present invention provides a new and improved method and apparatus for providing the user with immediate feedback of the electronic pen's trajectory.